Congestive heart failure (CHF) is a significant health problem and the prevalence of the disorder is increasing. CHF can cause cardiac output to decrease as the heart loses its ability to efficiently pump blood. In some cases of CHF, the left ventricle ceases to contract synchronously, causing pumping action of the heart to be significantly impaired. The increased size and reduced contractility of the left ventricle further exacerbate intraventricular dyssynchrony as the depolarization delays between portions of the left ventricle lengthen. The decrease in pumping ability can lead to blood accumulation throughout the body, which may damage other organ systems.
Cardiac pacing is increasingly prescribed as treatment for CHF. The evolution of pacing devices to treat CHF has progressed from dual chamber devices that pace the right atrium and right ventricle, to devices that provide bi-ventricular pacing, and most recently to devices that provide pacing at multiple sites within one heart chamber. Multi-site pacing serves to produce a more coordinated contraction within a heart chamber leading to improved pumping action.
Cardiac pacing involves delivery of electrical stimulation pulses (pacing pulses) to the heart. Pacing pulses of sufficient energy “capture” the heart tissue by initiating a propagating wavefront of depolarization at the pacing site that causes a contraction. The energy of pacing pulses delivered for pacing therapy should be set to an appropriate energy level that reliably achieves capture without unduly reducing the battery life of an implantable device.